The field of the invention is sporting goods and the invention relates more particularly to the sport of bowling.
It is well known that the thumb size of a bowler varies during bowling. Typically, it decreases slightly in size and the serious bowler would like to be able to adjust the size of the thumb hole to an optimum size during bowling.
Numerous methods have been used for accomplishing this desired result. One such method is shown in the Gaunt U.S. Pat. No. 4,892,308 where a threaded insert may be selected and screwed into a threaded liner. The liners may be removed and replaced with liners having different inside diameters. The Haza U.S. Pat. No. 4,778,178 has an insert with two telescoped tubes which may be rotated with respect to each other which changes the shape of the insert.
Another patent to Haza, namely U.S. Pat. No. 4,561,654, utilizes a flexible tube or sleeve which has a conical wedge on its outer surface. This wedge can either relax or constrict the diameter of the thumb hole. The Ginder U.S. Pat. No. 3,416,796 has a flexible tapered wall which can be moved inwardly and outwardly within an outer tapered member to increase or decrease the inside diameter of the thumb hole. The Bunk, et al. U.S. Pat. No. 3,012,783 has a flexible tube which may be expanded or contracted to change the inside diameter of the thumb hole. Lastly, the Darby U.S. Pat. No. 2,210,528 has a sleeve which is slotted at the top and which may be drawn down into the tapered thumb hole to reduce the thumb hole size.
Although these numerous attempts have made to provide a usable adjustable thumb hole, they have not successfully solved the problem and none have found widespread use.